BADWATER 135, CALIFORNIA USA
Traditionally referred to as 'the world's toughest foot race', Badwater was forced to alter its traditional route through Death Valley in 2013. The Death Valley Park authorities placed a ban on strenuous events taking place during the summer months, when air temperatures (in the shade) reach over 48 degrees. So organisers came up with an alternative route, one with more than 5,200m of cumulative vertical ascent (compared to 3,962 in the previous route), and 3,900m of cumulative descent (compared to 1,433m). While temperature might not reach the sizzling heights of Death Valley (ultra-runner Dean Karnazes once reported that between his team car handing him a cheese sandwich and him eating it, said sandwich became a toastie), the world's toughest foot race just got tougher.
Race facts: The race takes place in July; 135miles(217km); Maximum 48 hours, there is an entry fee.
DODO TRAIL, MAURITIUS
"Named after the bird that once inhabited Mauritius, where the race is set, it was apt that after scrambling up and down two mountains, my quads were almost extinct", reported one writer who ran the 25km version. This is a classic beauty-and-beast mountain race. Breathtaking views of forested peaks combine with more than 1,500m of ascent (3,500m in the 50km event) and a course profile that resembles a row of shark's teeth. "It's the only race in which I've felt fear, one misstep on the steep descents and you are out of the game", said one runner.
Race facts: The race takes place in July; 15.5/31miles (25km/50km); maximum 10/15hours, there is an entry fee.
YUKON ARCTIC ULTRA, CANADA
"In terms of mental toughness the Yukon is by far the hardest race I have done", says Bayliff, who ran the 300-mile version. "You're faced with the same scenery day after day. It's mind-numbing. The daylight is minimised, too. You get about six hours of it, and the rest of the time you're walking in darkness or semi-darkness. You start off freezing, but when you're pulling a pulk (sled) with 30kg in it, you get warm so you shed clothes so as not to sweat. In the arctic, though, your sweat can freeze and you can get hypothermia very quickly. The whole race is about body management. I did the Yukon as part of a team and we agreed that every 24 hours we were going to sleep for three and spend an hour doing the necessaries - eating, going to the toilet, putting the camp up and down. So we were walking for 20 hours a day, 10 days."
Race facts: it takes place in February; distances 42km, 100/300/430 miles, there is an entry fee.
ENDUROMAN ARCH TO ARC, LONDON TO PARIS
The clock starts when athletes leave London's Marble Arch for an 87-mile run to the Dover coast. Then it's a swim across the Channel to the French coast, where they embark on a 181-mile ride from Calais to the Arc de Triomphe in Paris. Only 18 solo athletes have ever finish the event (you can do it as a relay team), with 41-year-old Australia John van Wisse setting a new world record of 61 hours and 27 minutes. Hi did this record despite getting lost on the run and adding 4km to his route.
Race facts: distance 300 miles; duration 61 hours.
6633 ULTRA, CANADIAN ARCTIC
Named after the latitiude co-ordinates in minutes and dregrees of the Arctic Circle, the 6633 is a non-stop, self-sufficient race that claims to be the toughest, coldest, and windiest extreme ultra-marathon on the planet. Both the shorter and longer distances cross the line of the Arctic Circle in heavily subzero temperatures - but if you want to make sure that you do make it as far as a finish line, your best bet is to opt for the 120-miler. Only 11 people have finished the 350-mile race in its seven-year history.
Race facts: race takes place in March, 120/350 miles (193/563km), duration 3-4 days, there is an entry fee.
HARDROCK 100, COLORADO USA
This isn't just any 100-miler. It includes extreme altitude changes, taking runners through several climate zones. Long, steep climbs are its calling card, with runners taking on 13 major passes in the 12,000 to 13,000 foot range, while the rugged terrain includes snow packs, river crossings and boulder fields. It's a course designed to provide extreme challenges in altitude, steepness and remoteness, so endurance alone won't be enough to see you through. Add mountaineering, wilderness survival and wilderness navigation skill to your CV, and you might just make it through.
Race facts: race takes place in July; Distance 100 miles (162km); duration 48 hours maximum; there is an entry fee.
THE LAST DESERT, ANTARCTICA
The only multi-day stage race o the Antarctic, the event uses a polar expedition ship as its base. Each day athletes are taken from ship to shore by zodiac boats. Any one of 10 different locations on the around the Antarctic peninsula could be their destinations. Athletes have to deal with unpredictable stage lengths and start times. The race is only open to those who have finished at least two of the races in the 4 Deserts series (includes the Gobi March, Atacama Crossing and Sahara Race). It gives you more chance of surviving, apparently.
Race facts: race take place in November, distance 155 miles (250km); duration 7 days; there is a fee to enter.
ATACAMA CROSSING, CHILE
"The driest place on earth, 50-times more arid than Death Valley ant temperatures reach the high 40s (centrigrade) during the day," explains Simon Bayliff. "At night it drops to single digits, but just after you start each stage the sun rises and you start cooking. It's the altitude you fight with most. It affects breathing and sleeping, and your heart rate is constantly elevated. The terrain varies, with salt flats the most challenging. It's a crunchy and lumpy surface that sucks all the energy from your stride."
Race facts: race takes place in October; distance 155 miles (250km).
MARATHON DES SABLES, SAHARA DESERT MOROCCO
Now in its 29th consecutive year, this multi-stage race through the Sahara desert requires you to run the equivalent of five and a half marathon in six days, while carrying everything you need to survive on your back. The stages vary in length from 34km to 91km (potentially an overnight stage), although the route varies slightly every year and is kept secret until the day before the race starts. Heat is a serious factor here, with temperatures reaching almost 50 degrees centigrade, but athletes are only allowed to be put on an IV drip twice. Three times and you're out.
Race facts: race takes place in April; distance 156 miles (251km); duration 6 stages; there is an entry fee to enter.
THE JUNGLE ULTRA, CUSZCO PERU
"I count this as the toughest ultra, physically and emotionally", says Bayliff. "It's 40 degrees and 100 per cent humidity every day, so you're soaking wet from start to finish, you get chafing in places you would not know possible." The race starts at altitude and works its way down into the rainforest basin over the first few days. You're running on trails that have been cut out by indigenous people and are lined with huge roots and bamboo. Everything is alive spiders, ants, whatever, is there. It's best to keep going, the faster you run the less you see, to be afraid of.
Race facts: race takes place in June; distance 143 miles (230km); duration 5 stages, 5 days; there is an entry fee to enter.